It has long been known to protect building slabs from fire or high temperatures by providing their surfaces with alkali silicate paints optionally containing finely divided fillers such as slate flour (DE-AS 11 98 271) or other mineral flours DE-AS 14 71 020, DE 35 12 515). Also, known is the use of fire-protective slabs made of alkali silicates prepared by embedding silicate fibers into a layer of a silicate solution, optionally incorporating reinforcements of metal wire, and subsequently solidifying the layer by removal of water at elevated temperatures (DE-AS 14 71 005). In both cases, the water content of the slabs is high enough to allow formation of a foam layer of water glass which keeps heat away from the underlying structure in case of fire. However, due to their water content, such slabs, do not have sufficient weathering resistance and bending tensile strength. When used on external surfaces, they must be protected from water exposure by protective coatings.
Anhydrous coatings resistant to chemical, thermal and mechanical exposure are described in DE-OS 34 10 844. This specification discloses a coating mass made up of water glass, quartz, clay, lavalite, magnesium silicate, pumice, cement, and water which is applied to articles to be coated such as tank containers, water processing plants, pipelines, ships, and concrete buildings. Subsequent to prehardening, the mass is subjected to a fire melt treatment at temperatures of from 400.degree. to 1,900.degree. C.
DE-AS 27 32 387 describes a process for manufacturing insulating building slabs, wherein a slab of mineral fiber, prebound with an organic binder and having a density of 0.2 g/cm.sup.3, is soaked with an aqueous slurry of a binding clay. This is then subsequently dried at temperatures above 105.degree. C. and then tempered above 400.degree. C., with the temperature being maintained below the transformation temperature of the mineral fiber used. In such a process, one begins by using a slab of mineral fiber having a density as high as possible to obtain appropriate resistance properties. Thus, this process suffers from the drawback that mechanical strength must be achieved by employing high density material. Solutions to the problem of protecting building components from fire, linings or coatings for the articles to be protected have been constantly proposed.